package com.liwujie.utils;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

/**
 * 雪花算法ID生成器
 */
@Component
public class SnowflakeIdWorker {
    // 开始时间戳 (2025-01-01)
    private final long twepoch = 1735660800000L;

    // 机器ID所占的位数
    private final long workerIdBits = 5L;
    // 数据中心ID所占的位数
    private final long datacenterIdBits = 5L;
    // 支持的最大机器ID (2^5 - 1 = 31)
    private final long maxWorkerId = ~(-1L << workerIdBits);
    // 支持的最大数据中心ID (2^5 - 1 = 31)
    private final long maxDatacenterId = ~(-1L << datacenterIdBits);
    // 序列号所占位数
    private final long sequenceBits = 12L;

    // 机器ID向左移12位
    private final long workerIdShift = sequenceBits;
    // 数据中心ID向左移17位(12+5)
    private final long datacenterIdShift = sequenceBits + workerIdBits;
    // 时间戳向左移22位(5+5+12)
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

    // 生成序列的掩码(4095)
    private final long sequenceMask = ~(-1L << sequenceBits);

    // 工作机器ID(0-31)
    @Value("${snowflake.worker-id:0}")
    private long workerId;

    // 数据中心ID(0-31)
    @Value("${snowflake.datacenter-id:0}")
    private long datacenterId;

    // 毫秒内序列(0-4095)
    private long sequence = 0L;

    // 上次生成ID的时间戳
    private long lastTimestamp = -1L;

    public synchronized long nextId() {
        long timestamp = timeGen();

        // 如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退过
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(
                    String.format("时钟回拨 %d 毫秒，拒绝生成ID",
                            lastTimestamp - timestamp));
        }

        // 如果是同一时间生成的，则进行毫秒内序列
        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            // 毫秒内序列溢出
            if (sequence == 0) {
                // 阻塞到下一个毫秒，获得新的时间戳
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            // 时间戳改变，毫秒内序列重置
            sequence = 0L;
        }

        // 上次生成ID的时间戳
        lastTimestamp = timestamp;

        // 移位并通过或运算拼到一起组成64位的ID
        return ((timestamp - twepoch) << timestampLeftShift)
                | (datacenterId << datacenterIdShift)
                | (workerId << workerIdShift)
                | sequence;
    }

    // 阻塞到下一个毫秒，直到获得新的时间戳
    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    // 返回当前时间(毫秒)
    protected long timeGen() {
        return System.currentTimeMillis();
    }
}